Newbie- New mill with a makeshift mist coolant need advice.

[Matt.]

Hi,

This is my first post. I recently purchased a mill (Chinese) and have spent several days rebuilding it :-). My initial use for the machine will be milling 1-2mm aluminum plate and hopefully Circuit Boards.

After trial and error I have the machine cutting the aluminum (not melting it :-)) but still not with the finish I would like. I have attached some pictures and would love comments. You will see I added a air brush as a mist coolant which seems to work well with a mix of kero and cutting oil.

The machine specs are
1200mm x 800mm bed
2kw water cooled vfd.
mach3

The best cutting I have done so far is 6000rpm 200mm/min 15mm/m plunge with a 3mm, two flute slot drill. but still not great.

I believe that my vfd can do 12000rpm but at that melts not cuts.

Please advise.

Matt

[BobWarfield]

G-Wizard would run your 3mm at about 340 mm/minute feedrate at 6000 rpm.

I'm assume full slotting (3mm width of cut) and 0.35mm is about as deep a cut as you should make with that tiny endmill.

You can sign up for the G-Wizard Beta test if you want to experiment with more cutting scenarios. Link is my signature.

Cheers,

BW

[Matt.]

I used the slot drill to cut the entire depth of 1.7mm in one pass. Is that bad? I found that the tool work best when it cut completely through the material, it seem to remove the waste best then.

[BobWarfield]

Matt, it isn't necessarily bad. Was it a carbide endmill or HSS? My figures were based on HSS. Carbide could go deeper.

The thing is, you've got a pretty small diameter endmill. You can't stick it out very far or cut very deep before it will start to deflect. Part of what G-Wizard tries to do is calculate how much you can cut before the deflection starts to be a problem. Too much deflection yields an inaccurate cut, higher tool wear, chatter, and worse finish.

I don't really have all the data on what you're doing, so I took a lot of defaults to come up with the figure I gave. Getting all the parameters dialed in and optimized is going to take a little work. The good news is you've moved to the point where at least you're just trying to optimize the finish!

Cheers,

BW

[RomanLini]

May I ask about the machine Matt? How much was it delivered to Australia (I'm aussie too) and what did you have to do to get it working ok? I've heard some of those Chinese routers arrive all bent etc with smashed up packaging from someone being a bit rough with the heavy parcels during shipping.

I cur aluminium with my router using 3mm endmill, and based on my (limited) experienced it looks like you are doing a few things wrong. Your chips look like dust and your cuts are ragged...

Try cutting at about 9000 or 10000 RPM with a 3 flute or even 4 flute endmill (I usually use Sutton 4 flute these days because I can buy easy locally and the 4 flute seem stronger ie more rigid in the tool itself). I use 0.5mm depth for each cut and speed of about 9mm to 12mm per second (540mm/min to 720mm/min). This is much faster than you are going so it won't be putting the heat into the same place in the stock for very long, and the lighter cuts mean the material is fully supported all around while you are cutting, so you get a much better finish. It also means less clogging of the groove as you cut because with shallow cuts the chips are thrown out easier.

Otherwise some small tips like cutting 0.5mm deep on each piece then moving to the next piece, this allows the stock time to cool and gives you time to brush out the chips and re-lube etc while it is doing the 0.5mm cut on the next piece.

And at the end leave about 0.05 mm of "skin" left ie don't cut out the pieces all the way through. This holds them in place to the end and gives a better finish as it won't lift the stock as happens when you cut through.

My machine is a bit more rigid than yours although it is only a home made job with router spindle but even so I think those speeds will work ok with your 3mm endmill.

By the way, what are the doodads you are making?

[Matt.]

Sure it cost just under 3K landed including the spindle. Where abouts in Australia are you. If you are in Sydney you are most welcome to come have a look. I tried a 0.4mm cut at 500mm/Min and the results are better. I still need to do some work on my machine though. The y axis is not as smooth as I would like. I think I have some misalignment in the bearings. Also I think I have to move my spindle further into its mount so there is not so much turning force on Y axis when plunging in the X.

[RomanLini]

Thanks for the offer to pop in and take a look, but I'm in godzone country about 17 hours north of you so it's a little far to travel.

It's probably worth beefing up that Y axis a little, from what I can see in your photos the Y axis on the gantry looks to have unsupported rails, so if you are serious about cutting out the small doodads (you still didn't say what they are??) you could fix them close to the edge of the machine so the Y rail flex will be minimal, as the rails flex most in the middle of course. You could even affix a temporary rails clamp on the middle of those Y rails if you are doing production runs, provided the doodads are small and near the side of the machine (as I said) and it doesn't require full Y travel to cut them.

Moving the spindle inwards can help a lot, my CNC machine was custom designed to have very good geometry and getting that spindle mounted inwards was one of the goals. You can see my build thread here;
DIY hobby small plastics mill/router if you want to check it out.

Anyway I'm glad you got the cutting problem mostly sorted! You may need to get a brand new tool if that first one saw some heat/chipmelt and got a bit blunted.

[Matt.]

RomanLini,

I checked out the post on your router build. Where are the photo's :-) I too am an electronics enthusiast. That is part of why I brought the mill. The widgets in my photos are just end plates to project enclosures. I hope to be able to do so professional looking low production run designs.
I think I have some major mis-alignment problems especially in the longest axis Y. I loosened off the bearings and shifted them a little which has helped but I still think I am loosing steps occasionally. Is there any good procedure for aligning the ball screw, bearings etc?
I also need some better nuts for the fixed bearings. The ones supplied where just chrome dipped regular nuts. I need to get some with the little grub screw in.
I will send you some more photos so you can have a sticky. I appreciate your advice.

Matt.

[Matt.]

Sorry Roman I found the photos. Nice little machine you have there.

[RomanLini]

Thanks! My machine has been a good little workhorse.

Sorry I can't suggest much with your alignment other than the usual basics; ie disconnect the motor and screw so you just have the rails. Then slide by hand and feel if it is binding. Then align one rail as square and fix it, and the align the secondary rail so it doesn't bind.

Once it is sliding nicely, you can mess with the motor/leadnut/screw setup. That depends on what parts are adjustable. I like to align the motor to the nut, with the axis as close to the motor as possible and no binding. Then move it to theother end of the travel and align the end mount for the screw to the nut. Ideally that should be enough but sometimes you have to fiddle a bit.

One of my axes is a bit stiff until the machine warms up, ie it was aligned at operating temp. I just warm the machine up before use but I've been contemplating adding fixed temp regulation to the metal frame of the machine or put it in a cabinet with a fixed temperature air pumped in which I think might be the better option.

I didn't get what you meant by the nuts need grub screws, maybe you could post more photos. There's some things I like about those Chinese machines and I've been contemplating getting one for a while and fixing it up (like you are doing). I think one of those little Chinese machines (smaller than yours) might be good as a aluminium router if set up with flood coolant and at a 45' angle to flush chips out, and a bit of frame strengthening etc. My machine cuts alloy great but I hate the cleanup of all the little gritty greasy chips stuck to everything haha.

Please put photos in this thread (not send them to me) as other people will read and may have suggestions too!